A radiation indicator device which provides a visually recognizable indication of exposure to ultraviolet radiation.
Sunlight is normally divided into infrared energy, visible light, and ultraviolet light. Infrared energy consists of the portion of the solar spectrum, with wavelength above 760 nanometers. Visible light is defined as radiation with a wavelength between 400 and 760 nanometers. Ultraviolet light consists of radiation with a wavelength below 400 nanometers. Infrared energy is our main source of warmth. Sunlight supplies energy necessary for photosynthesis in living plants. In fact, it is essential for all living things on earth.
In leisure time, some people like to bask in the sun to get a healthy looking tan. Many people like to enjoy months of uninhibited sunshine exposure while participating in other outdoor activities. However, research has found that increased exposure to ultraviolet rays from the sun causes skin cancer, cataracts in human eyes, sunburn, skin wrinkling, possible immune system damage, and leathery skin. It also causes cacti to shrivel, cattle and sheep to develop conjunctivitis, eucalyptus trees to turn yellow, frog population to decline, and fish population to decrease. Humans are among the living beings most vulnerable to the constant shower of ultraviolet radiation. Unprotected by scales or feathers, we face a rising threat of illness related to sunlight exposure. The new health hazard is challenging our desire to spend time outdoors. The incidence of skin cancer has been on the rise steadily for the last 20 years and this disease has become one of the leading causes of death today. One in six Americans might develop skin cancer in their lifetime because sun damage to the skin is cumulative.
Hovering six to 25 miles above the earth, the stratospheric ozone layer is our natural sunscreen, protecting us from some of the sun""s harmful rays. Atmospheric scientists at National Aeronautics and Space Administration have used satellites to study the depletion of ozone in the upper atmosphere. There is evidence that a severe depletion of the ozone layer has occurred over the Antarctic, resulting in an ozone hole of about 9 million square miles in 1994 (about 2.5 times the size of the United States of America). The hole in the ozone layer is caused by chlorofluorocarbons (CFCs) which are commonly used as refrigerant and propellant in aerosol sprays. The CFCs undergo a series of chemical reactions in the atmosphere, leading to the production of chlorine monoxide that consumes ozone. Levels of ozone destroying chlorine monoxide in Antarctic are extremely high by August and as a result the ozone shield is destroyed allowing damaging solar ultraviolet radiation to reach the earth""s surface. Although the thinning of the ozone layer is most severe over Antarctica, it has been observed as a global phenomenon at all latitudes. According to a report of the United Nations, during the last decade the annual dose of harmful ultraviolet light striking the Northern Hemisphere rose by about five percent.
The solar ultraviolet spectrum is generally considered to consist of wavelengths between 100 and 400 nanometers and the International Commission on Illumination further subdivides this portion of the solar spectrum into UV-A, UV-B and UV-C rays.
UV-A rays have the longest wavelength in the range of between about 400 nanometers and about 315 nanometers and these rays penetrate the skin the deepest. UV-A light is also the most difficult to screen out. These wavelengths of ultraviolet radiation pass readily through the atmosphere and maintain their intensity throughout the day regardless of the position of the sun above the horizon. Heavy clouds can filter this radiation but many traditional sunscreen formulations do not adequately protect against UV-A exposure.
UV-B rays are in the wavelength region of between about 315 nanometers and about 280 nanometers. Although ozone and clouds screen out some of them, many of them do reach the earth. UV-B light is responsible for wrinkling, breaking down the elastic tissue and collagen, and sunburn. UV-B light is probably 100 times more carcinogenic than UV-A light. It causes three types of skin cancer-basal cell cancer, squamous cell cancer, and melanoma. Skin cancers have skyrocketed in the last 20 years, coinciding with our increased outdoor activities and with the depletion of the ozone layer. UV-B light is in large part responsible for the tough leathery look of human skin following prolonged outdoor weathering. However, when the ozone layer is thick enough to function properly, it shields us from most UV-B rays.
UV-C rays have the shortest wavelength of between about 280 nanometers and about 100 nanometers. These rays are the most dangerous ultraviolet radiation but they are filtered out by the atmosphere and do not reach the surface of the earth.
In the United States, the National Weather Service, urged by the Environmental Protection Agency, the Centers for Disease Control, and the American Cancer Society, has begun a new index of UV radiation to warn people against overexposure to the sun. This Ultraviolet Potential Index is based on atmospheric changes and has a scale from 0 to 15. The higher the number, the higher the risk to skin cancer and the faster that outdoor enthusiast will burn. To predict the Ultraviolet Potential Index, the National Weather Service uses satellites and ground equipment to compute the UV levels through a combination of readings from forecasted cloud cover, temperatures, and local ozone amounts. The more ozone present at a location, the less radiation will reach the earth""s surface at that area. A rating of 7 means that fair-skinned people should stay out of the sun or risk sunburn and other skin damage associated with high UV exposure.
The new Ultraviolet Potential Index measures potential exposure in five levels according to the National Weather Service and the American Cancer Society:
0 to 2: Minimal risk of ultraviolet radiation; could be in sun unprotected for more than an hour without skin burning;
3 to 4: Low risk; could be in the sun unprotected for 30 minutes to an hour;
5 to 6: Moderate risk; could be in sun unprotected for 20 to 30 minutes;
7 to 9: High risk of skin damage at 13 minutes;
10 to 15: Very-high risk of skin damage occurs at less than 13 minutes.
Although an effective method of defining the risk associated with sun exposure, the Ultraviolet Potential Index has a variety of limitations as a method to protect the population from skin damage due to ultraviolet radiation. As of July 1994, only 85 cities in the United States were given the predicted Ultraviolet Potential Index on a trial basis. It would be very difficult to include all parts of the nation. These predicted index numbers could only serve as general guidelines since the local cloud cover might move away or become thick because weather conditions are unpredictable. Thus, there is a need for a device to be used in situ that would indicate ultraviolet radiation levels and consequently warn outdoor enthusiasts against overexposure to the sunlight anywhere and at any time.
To reduce the ultraviolet radiation exposure to the skin it is advisable to apply sunscreen having a Sun Protection Factor (SPF) of at least 15 and above. The sunscreen contains ultraviolet light absorbers, which are designed to remove part or most of the harmful ultraviolet rays. By applying the sunscreen on the skin, one might mistakenly believe that the skin will not be damaged by the ultraviolet light. In fact, the sunscreen does not completely block all UV-A and UV-B rays in the sunlight. The skin has no natural sensors to ultraviolet radiation exposure other than the delayed and painful effect of skin erythema or xe2x80x9csunburnxe2x80x9d which follows excessive exposure.
Various systems and devices have been proposed for monitoring exposure to ultraviolet radiation, such as those disclosed in U.S. Pat. No. 3,449,572 (Sylvester et al) U.S. Pat. No. 3,787,687 (Trumble), U.S. Pat. No. 3,903,423 (Zweig), U.S. Pat. No. 4,130,760 (Fanselow et al), U.S. Pat. No. 4,308,459 (Williams), U.S. Pat. No. 4,788,433 (Wright), U.S. Pat. No. 4,829,187 (Tomita et al), U.S. Pat. No. 4,985,632 (Bianco et al), U.S. Pat. No. 5,028,792 (Mullis) and U.S. Pat. No. 5,117,116 (Bannard et al).
However, many of these systems and devices have various drawbacks including use of cumbersome mechanical devices, use of carcinogenic compounds for indicating exposure by colour indication, or the like. In addition, some devices have limited utility if they do not respond predominantly to the UV-B part of the solar spectrum. Devices which respond to both UV-A and UV-B could give misleading indications of potential harm.
Other systems and devices have been proposed generally for indicating exposure to radiation, including U.S. Pat. No. 3,051,837 (Nitka), U.S. Pat. No. 3,290,499 (Vale et al), U.S. Pat. No. 3,691,380 (Hubner et al), U.S. Pat. No. 3,743,846 (Matsumoto et al), U.S. Pat. No. 3,899,677 (Hori et al), U.S. Pat. No. 4,008,085 (Lemahieu et al), U.S. Pat. No. 5,051,597 (Lewis et al), U.S. Pat. No. 5,084,623 (Lewis et al) and U.S. Pat. No. 5,099,132 (Ueno et al).
Many of these systems and devices are directed at the indication of radiation outside the ultraviolet range or are directed at photographic processes rather than the indication of radiation.
There is therefore a need in the art of radiation indicators for an indicator device which provides a visually recognizable indication of ultraviolet radiation exposure, particularly ultraviolet radiation exposure which is potentially harmful to human skin.
The present invention relates to a device for indicating exposure to ultraviolet radiation, which device is inexpensive, disposable and is self-contained, requiring no other device or indicator in order to ascertain radiation exposure levels.
The invention is a radiation indicator device which is comprised of a radiation sensitive mixture which undergoes a colour change which is visually recognizable when exposed to ultraviolet radiation. The device may also comprise a graphic pattern interspersed amongst the radiation sensitive mixture, which graphic pattern provides a reference for quantifying the amount of radiation exposure.
In a first aspect, the invention is a radiation indicator device for use in indicating exposure to ultraviolet-B radiation, the indicator device comprising:
(a) a radiation sensitive mixture selectively responsive to ultraviolet radiation having a wavelength substantially within or shorter than the range of wavelengths of ultraviolet-B radiation, the radiation sensitive mixture being comprised of:
(i) an amount of an organic halogen constituent capable of producing at least one acidic product upon exposure to ultraviolet radiation; and
(ii) an amount of an indicator constituent capable of producing a change in colour in response to a change in concentration of the acidic product, so that the radiation sensitive mixture has a first colour representing a relatively low concentration of the acidic product and has a second colour representing a relatively high concentration of the acidic product; and
(b) a graphic pattern interspersed amongst the radiation sensitive mixture, the graphic pattern having a graphic pattern colour substantially identical to one of the first colour and the second colour of the radiation sensitive mixture, the graphic pattern being visually distinguishable from the radiation sensitive mixture when the indicator constituent is not at the other of the first colour and the second colour.
The graphic pattern colour is preferably substantially identical to the second colour of the radiation sensitive mixture so that the graphic pattern becomes less visually distinguishable as the radiation sensitive mixture approaches the second colour. The graphic pattern colour may however be substantially identical to the initial colour so that the graphic pattern becomes more visually distinguishable as the radiation sensitive mixture approaches the second colour.
In a second aspect, the invention is an indicator device for use in indicating exposure to ultraviolet-B radiation, the indicator device comprising a radiation sensitive mixture selectively responsive to ultraviolet radiation having a wavelength substantially within or shorter than the range of wavelengths of ultraviolet-B radiation, the radiation sensitive mixture being comprised of:
(a) an amount of an organic halogen constituent capable of producing at least one acidic product upon exposure to ultraviolet radiation; and
(b) an amount of an indicator constituent capable of producing a change in colour in response to a change in concentration of the acidic product, so that the radiation sensitive mixture has a first colour representing a relatively low concentration of the acidic product and has a second colour representing a relatively high concentration of the acidic product, wherein the first colour is visually distinguishable from the second colour.
The first colour may be visually distinguishable from the second colour in any manner. For example, the first colour may be a completely different colour than the second colour or the first colour and the second colour may be significantly different hues of the same colour.
The organic halogen constituent may be comprised of any organic halogen compound or compounds including substituted organic compounds which are capable of producing the acidic product upon exposure to ultraviolet radiation.
Preferably the organic halogen constituent is selectively responsive to exposure to ultraviolet radiation having a wavelength substantially within or shorter than the range of wavelengths of ultraviolet-B radiation. Alternatively or additionally, the radiation sensitive mixture may be comprised of a screen or a screening agent for inhibiting the exposure of the organic halogen constituent to radiation other than radiation having a wavelength substantially within or shorter than the range of wavelengths of ultraviolet-B radiation. Preferably the selectivity of the radiation sensitive mixture is substantial so that the responsiveness of the radiation sensitive mixture to radiation other than radiation having a wavelength substantially within or shorter than the range of wavelengths of ultraviolet-B radiation is minimized.
Although not essential to the invention, the radiation sensitive mixture may be designed also to inhibit its responsiveness to radiation having a wavelength shorter than the range of wavelengths of ultraviolet-B radiation in order to minimize potential responsiveness to ultraviolet-C radiation.
The organic halogen constituent is preferably a relatively stable substance or substances. In addition, the organic halogen constituent is preferably relatively inexpensive and is either commercially available or is relatively easy to produce. The organic halogen constituent is therefore preferably a relatively simple substance both chemically and structurally.
As a result, preferably the organic halogen constituent is comprised of an aliphatic halogen compound comprising between one and five carbon atoms and one or more halogen atoms, an aromatic halogen compound comprising one or two aromatic rings and one or more halogen atoms, or a cyclic aliphatic halogen compound comprising one or more halogen atoms. The organic halogen constituent may be comprised of one or more than one compound. The halogen atoms are preferably chlorine, bromine or iodine. The cyclic aliphatic halogen compounds may be comprised of adamantanes.
Preferably, the organic halogen constituent is comprised of a compound selected from the group of compounds consisting of carbon tetrabromide, iodoform, chloral, bromal, 2,2,2-tribromoethanol, 1,2-dibromotetrachloroethane, hexachloroethane, trichloroacetic acid, a sodium salt of trichloroacetic acid, phenyl tribromomethylsulfone, phenyl trichloromethylsulfone, 1,2,4,5-tetrabromobenzene, 1-bromoadamantane, 1,3-dibromoadamantane, 2-bromoadamantane and 1-iodoadamantane. More preferably the organic halogen constituent is comprised of a compound selected from the group of compounds consisting of carbon tetrabromide, bromal, 1,2-dibromotetrachloroethane, hexachloroethane, 1,2,4,5-tetrabromobenzene, 1,3-dibromoadamantane and 1-iodoadamantane. Most preferably the organic halogen constituent is comprised of a compound selected from the group of compounds consisting of 1,2-dibromotetrachloroethane, hexachloroethane, 1,2,4,5-tetrabromobenzene and 1-iodoadamantane.
The indicator device may be provided in any form. Preferably the indicator device is further comprised of a support having an indicator surface, wherein the radiation sensitive mixture is carried as a mixture layer on the indicator surface and wherein the graphic pattern is carried as a graphic layer on the indicator surface.
The graphic pattern may be comprised of an illustration, text, or both illustration and text. The illustration may depict an object or may comprise a design, including an abstract design.
The graphic pattern may overlay the radiation sensitive mixture or the radiation sensitive mixture may overlay the graphic pattern so that one of the graphic layer and the mixture layer is carried directly on the indicator surface and the other of the graphic layer and the mixture layer is carried indirectly on the indicator surface. Alternatively, both the graphic layer and the mixture layer may be carried directly on the indicator surface by providing gaps in the mixture layer. In the preferred embodiment, the graphic layer comprising the graphic pattern overlays the mixture layer comprising the radiation sensitive mixture so that the mixture layer is carried directly by the indicator surface and the graphic layer is carried indirectly by the indicator surface.
In the first aspect, the indicator constituent is selected so that the graphic pattern will be visually distinguishable when the radiation sensitive mixture is at either the first colour or the second colour. In the second aspect, the indicator constituent is selected so that the first colour is visually distinguishable from the second colour.
Any compound capable of producing a change in colour in response to a change in concentration of the acidic product and which meets the above criteria may be used as the indicator constituent. For example, the indicator constituent may be comprised of one or more compounds listed in the Sigma-Aldrich Handbook of Stains, Dyes and Indicators (Aldrich Chemical Company, Inc., Milwaukee, Wis., 1990). Representative examples include methyl orange, methyl red, aniline blue, methylene blue, congo red, methyl yellow, phenol red, phenolphthalein, bromocresol purple, chlorophenol red, ethyl orange, bromocresol green, and bromochlorophenol blue. Methyl orange and methyl yellow are among the preferred compounds which may be used as the indicator constituent. In the preferred embodiment the indicator constituent is comprised of methyl orange.
The radiation sensitive mixture is preferably further comprised of an amount of a binder for providing a matrix for the organic halogen constituent and the indicator constituent. The binder may be comprised of any compound which will provide the matrix without interfering significantly with the production of the acidic product, the change in colour of the indicator constituent or the selectivity of the radiation sensitive mixture.
Preferably the binder is comprised of an organic polymer or an organic copolymer. In the preferred embodiment the binder is comprised of polyvinyl chloride or one of the Geon(trademark) copolymers such as Geon(trademark) 136. Other organic polymers and copolymers such as for example polymers of cellulose derivatives, vinyls, acrylics and carbonates may however be used.
The radiation sensitive mixture may be formed by combining the organic halogen constituent, the indicator constituent and the binder. Preferably however the binder is dissolved or dispersed in an amount of a solvent to assist in the formation of the matrix of the radiation sensitive mixture. Preferably the solvent evaporates following preparation of the radiation sensitive mixture. Many substances may be effective as solvents for the binder, as long as they do not interfere significantly with the production of the acidic product, the change in colour of the indicator constituent or the selectivity of the radiation sensitive mixture. Preferably the solvent is comprised of tetrahydrofuran, acetone, 2-butanone, toluene, 1,4-dioxane, methylene chloride, chloroform, isopropanol, methanol or ethanol. In the preferred embodiment the solvent is comprised of tetrahydrofuran or tetrahydrofuran mixed with some other solvent such as acetone.
The radiation sensitive mixture may be further comprised of an amount of a surfactant for enhancing the dispersion of the indicator constituent in the binder. Many substances may be effective as surfactants as long as they do not interfere significantly with the production of the acidic product, the change in colour of the indicator constituent or the selectivity of the radiation sensitive mixture. Preferably the surfactant is comprised of Triton(trademark) X-100, reduced Triton(trademark) X-100, Niaproof(trademark) Type 4 or Tween(trademark) 20. Most preferably the surfactant is comprised of Triton(trademark) X-100.
The radiation sensitive mixture may be further comprised of an amount of a suppressing agent for suppressing an increase in concentration of the acidic product. Many substances may be effective as suppressing agents as long as they do not interfere significantly with the production of the acidic product, the change in colour of the indicator constituent or the selectivity of the radiation sensitive mixture. The suppressing agent is preferably comprised of a base, a buffer or a mixture thereof. Most preferably the suppressing agent is comprised of sodium maleate, zinc stearate, diphenylamine or related amines, a phosphate or a borate.
The radiation sensitive mixture may be further comprised of an amount of a promoter for enhancing an increase in concentration of the acidic product. Many substances may be effective as promoters as long as they do not interfere significantly with the production of the acidic product, the change in colour of the indicator constituent or the selectivity of the radiation sensitive mixture. The promoter is preferably comprised of an amine or other suitable nitrogen containing compound, such as a quaternary nitrogen compound. Most preferably the promoter is comprised of tetrabutylammonium iodide or diphenylamine.
The selectivity of the radiation indicator may be provided or may be enhanced by being further comprised of a screen or a screening agent for inhibiting exposure of the radiation sensitive mixture to radiation other than ultraviolet-B radiation. The screen may be comprised of a screening layer which overlays the mixture layer. Many substances may be effective as screening agents as long as they do not interfere significantly with the production of the acidic product or with the change in colour of the indicator constituent. The screening agent is preferably comprised of a compound such as Parsol(trademark) (4-(1,1-Dimethylethyl)-4xe2x80x2-methoxydibenzoylmethane), phorone, menthyl anthranilate, 2-hydroxy-4-methoxybenzophenone, 2,2-dihydroxy-4-methoxybenzophenone or 2-aminobenzophenone.
Finally, the radiation sensitive mixture may be further comprised of an amount of a plasticizer for enhancing the properties of the binder. Many substances may be effective as plasticizers as long as they do not interfere significantly with the production of the acidic product, the change in colour of the indicator constituent or the selectivity of the radiation sensitive mixture. The plasticizer is preferably comprised of dibutyl phthalate, dioctyl phthalate, trioctyl trimellitate, epoxydized soybean oil, triphenyl phosphate or 1,2-epoxydodecane.
The constituents of the indicator device and their concentrations may be selected in order to achieve a desired response to exposure to ultraviolet-B radiation. The concentrations of the organic halogen constituent and the indicator constituent may facilitate control over the specific hues of the first colour and the second colour as well as over the amount of radiation which is necessary to change the radiation sensitive mixture from the first colour to the second colour. In addition, the use of a screen or screening agent can provide or enhance the selectivity of the indicator device with respect to ultraviolet-B radiation. Finally, the use of a suppressing agent and/or a promoter and control over their amounts may facilitate custom designing of the device for different skin types.